Learning notes for Python

I just got started python, So write a summary that is easy to forget , I hope that's helpful . The editor I use is IDLE.

1. One can check all python Operation of functions in

dir(__builtins__)

Use interactive mode , Then enter this function , You can come out python All functions .

2. When exchanging two numbers , You can use the following code directly

x,y = y,x

The principle of this and x,y,z = 1,2,3 One principle .

3. stay IDLE in , Press Alt+P It means the last sentence , You can return the code of the previous sentence .

4. Escape characters are those that begin with \ Start character , as follows ：

5.""" """: This means that , Whatever is written in it will be output as is .

6. The result of adding characters to characters indicates the connection , for example ：

'520' + '1314'

The output of is 5201314

7. The result of multiplying a character by a number indicates copying , for example ：

' Hey, hey, hey ' * 1000

It's copying 1000 I mean

8. Press ctrl + C You can force the execution of a program to stop .

9.break sentence ： The function is to jump out of a layer of circular body .

10.import It means import , If we want to generate random numbers at random , Import required random modular .

import random

11. The function of random number is （ The latter two numbers represent the range of random numbers ）：

random.randint(0,100)

  This function can be attacked , in other words , Make its number not random , But reappearance .

x = random.getstate()
random.randint(1,10)
8
random.randint(1,10)
6
random.randint(1,10)
2
random.randint(1,10)
10
random.randint(1,10)
3
random.randint(1,10)
2
random.randint(1,10)
6
random.setstate(x)
random.randint(1,10)
8
random.randint(1,10)
6
random.randint(1,10)
2
random.randint(1,10)
10
random.randint(1,10)
3
random.randint(1,10)
2
random.randint(1,10)
6
random.randint(1,10)
4
random.randint(1,10)
8

Above , That is to say .

12. Numeric type ： Integers , Floating point numbers , The plural

Because of the high precision of floating point numbers , You need to use the following function to add floating-point numbers accurately

a = decimal.Decimal('0.1')
b = decimal.Decimal('0.2')
print(a + b)
0.3

It can also be compared ：

c = decimal.Decimal('0.3')
a + b == c
True

‘E Notation ’ That is what we usually call scientific counting , Used to represent some extreme numbers . for example ：

0.00005 == 5e-05

The plural ： We can go through x.real To get the value of its real part , adopt x.imag To get the value of its imaginary part . A complex number is also a floating point number .

Some operations on numbers ：

operation result x//yx Divide y Result （ Floor removal ）divmod(x,y) return （x//y,x%y）abs(x)x The absolute value of int（x） take x Convert to integer float(x) take x Convert to floating point number complex(re,im) Returns a complex number ,re Is the set of real Numbers ,im It's an imaginary number c.conjugate() return c The conjugate complex of pow(x,y) Calculation x Of y Power x ** y Calculation x Of y Power

What is the floor except ？ Is to ensure that the result of dividing two numbers is an integer . If it's not an integer , Just round down ( Take the largest integer smaller than the target result ）. for example ：

-3 // 2 == -2
3 // 2 == 1

Besides ,pow Supports three parameters , In fact, it is equivalent to the power operation of the first two parameters , Take the remainder of the third number , for example ：

pow(2,3,5) == 3

13. Boolean type （ In fact, it is a special integer type ）

The result is false The situation of ：

（1） Defined as False The object of ：None and False

（2） The value is 0 The number type of ：0,0.0,0j,Decimal(0),Fraction(0,1)( This means that the molecule is zero , A rational number whose denominator is one ）

（3） Empty sequences and sets ：'',(),[],{},set(),range(0)